Add Hidden Objects

It was really confusing to program in Flash because I remember a little bit of programming info. I didn't remember how to program my hidden object game so I chose to look on the Wiki for help. I would like to add a highlighter to my hidden objects. I want it to be hard to find but, every time I try to make it hide , it looks like it's not even there. I want to use the highlighter so that when people think they found it they can scroll over it and see if that's where the object is hidden. Since this is a starter game ,I'm going to try my best to make it hard, but at the same time fun.